This invention is directed to a method for separating kish graphite from fume in kish graphite-fume mixtures and recovering the kish graphite as a clean usable product.
Kish graphite is defined as single crystals of flake graphite which precipitate from super saturated solutions of carbon in iron as the molten iron cools during tapping, pouring, teeming or other operations during production of iron and steel. Kish graphite is formed, for example, when iron which is tapped from a blast furnace cools while flowing in a network of runners on a cast house floor to submarine ladles. Kish graphite also forms when iron is transferred from submarine ladles to a holding mixer or ladle in reladling stations where the iron is stored prior to its use as a charge material for steel producing furnaces. The kish graphite forms on or floats to the surface of the molten iron and is emitted from the hot surface in the form of fine particles. Kish graphite is very light in weight, hence the kish graphite is carried into the atmosphere by heat convection from the surface of the molten iron.
Another product of the aforementioned operations is "fume". Fume is released from the molten metal at the same time as the kish graphite. Fume consists of relatively fine particles of iron oxides, silica, alumina, zinc oxide, manganese oxides, lime, magnesia and the like. Since kish graphite and fume are released from the molten metal at the same time, mixtures of kish graphite and fume are formed. The formation of large quantities of kish graphite-fume mixtures causes serious storage and disposal problems in steel plants. It is recognized that both kish graphite and fume are valuable commodities in themselves. Kish graphite can be used in the production of carbon electrodes, carbon electrical brushes, graphite crucibles and the like. However, the kish graphite must be relatively pure, that is, free from contaminating materials. Fume can be used as charge material to metallurgical furnaces, such as blast furnaces, wherein the iron oxides can be reduced to metallic iron. The fume must be balled, that is, formed into roughly spheroidal-like particles of a desired size or sintered prior to use in the metallurgical furnaces. The presence of large quantities of kish graphite in the mixtures makes kish graphite-fume mixtures unsuitable for balling. There is, therefore, a need for a method of separating kish graphite from fume in kish graphite-fume mixtures and recovering kish graphite which is substantially free from fume and which kish graphite retains its original size. Prior art methods to separate kish graphite from fume, include one method described in U.S. Pat. No. 1,239,992 issued Sept. 11, 1917 to Frederick W. Weissmann in which graphitic carbon is separated from iron and iron oxides and silica. In order to rid the graphite flakes of iron and silica, the mixture is reduced to powder and graphitic carbon separated from the iron and silica by levitation. The comminuted graphitic carbon is chemically refined by boiling with sulfuric and nitric acids or hydrochloric and hydrofluoric acids. While a clean kish graphite may be obtained by this method, the kish graphite loses its original size and shape during comminution.
It is therefore the object of this invention to provide a method for separating, cleaning and recovering kish graphite from mixtures containing kish graphite and fume.
It is another object of this invention to provide a method for separating kish graphite from fume in kish graphite-fume mixtures and recovering cleaned kish graphite wherein the kish graphite is washed in a solution of a washing agent and a non-ionic or cationic surface active agent and the kish graphite is separated and recovered as filter cake by filtering the mixture of kish graphite, washing agent and surface active agent.